Aligned dowels in chair seat cause cup?

In Sam Maloof's dvd he explains that he staggers the line of dowels across the seat (at the front end only presumably because it is thinner) to avoid the five joined boards cupping. So the four dowels line up like this: - _ - _ rather than like this: - - - -

Does anyone have experience of this cupping happening, due to the aligned dowels, or an explanation of why it would happen?

I have made many large flat surfaces, tables etc and never had them cup (I only ever use dowels as Sam did). I have a video of him saying the same thing and I can see the thinking behind it but I have never bothered to off set them. Sometimes we can just get an idea in our heads and run with it. Maybe thats what happened with Sam. Although it could happen I guess, given the right circumstances.

The only reason I can think off for staggering the dowels in a seat is that the dowels might be touching/almost touching if they were in line. In a table the boards would be much widwe and therefore this would not be an issue. Only a guess though.

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Originally Posted by BobR

The only reason I can think off for staggering the dowels in a seat is that the dowels might be touching/almost touching if they were in line. In a table the boards would be much widwe and therefore this would not be an issue. Only a guess though.

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He says cupping is the reason. And boards are about 100mm wide

JB I must be missing something. Are you saying five boards at 500mm wide - that is 2.5 metres. I would suspect that 500 metres is the total width of the seat making each board only 100mm wide. Then depending on the length of each dowel you have less than 50mm each side.As I said in my previous post, I am only guessing as to the reason for the cupping.

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Originally Posted by BobR

JB I must be missing something. Are you saying five boards at 500mm wide - that is 2.5 metres. I would suspect that 500 metres is the total width of the seat making each board only 100mm wide. Then depending on the length of each dowel you have less than 50mm each side.As I said in my previous post, I am only guessing as to the reason for the cupping.

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I meant 100mm; now corrected.

This is touching the memory as to where the dowels are installed but when the seat is shaped would not the front dowels start to show if they were in the top part?

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Originally Posted by Christos

This is touching the memory as to where the dowels are installed but when the seat is shaped would not the front dowels start to show if they were in the top part?

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The stagger is towards the rear, not vertical

I have no idea why this method would reduce cupping, but if you think of nailing or screwing timber togheter they are alway staggered . On thin material it helps with the timber splitting but more to the point it would be "dressing" the joining method
les